CHAPTER XI. 



CLASS REPTILIA.* 



Cold-hlooded, usually scaly Vertebraia, with a rigid and a left 

 aortic arch, a single occipital condyle, and pulmonary respiration. 

 The ovum is large and meroblastic, and the embryo has an amnion 

 and allantois. 



The class Reptilia is represented at the present day by lizards, 

 snakes, turtles, tortoises, crocodiles, and the New-Zealand 

 lizard, Sphenodon. These however are but a very small pro- 

 portion of the whole class. The extinct groups, which are almost 

 confined to the secondary period of geological history, form by 

 far the most important part of the class both in variety of struc- 

 ture and habit, and in strangeness of form. Of the living groups 

 the lizards and snakes are almost entirely terrestrial, and not 

 found fossil earlier than the tertiary period and then only in 

 small numbers ; the Chelonia and Crocodilia, which are partly 

 aquatic, date from the beginning of the secondary period, Avhile 

 Sphenodon is the representative of a sub-order which made its 

 appearance in the Permian and has persisted to the present day. 



Among the extinct forms we find the whale-like marine 

 Ichthyosauria, the bird-like flying Pterosauria, the huge bipedal 

 Dinosauria, and the mammal-like Anomodontia. It is a signi- 

 ficant fact that some of the most highly specialized and ancient 

 of the Reptilia, such as the Chelonia and Pterosauria, make theu' 

 first appearance with all their special characters fully developed ; 

 and in none of the eight sub-classes can it be said that the earliest 

 forms are definitely annectant to other sub-classes. 



* For literature of living forms see the subclasses. For extinct forms 

 see Zittel, Grundzuge der Palaeontologie, Leipzig, 1895, and the same trans- 

 lated into English, 1902, Macmillan & Co., London. A. S. Woodward, 

 Vertebrate Palaeontology, Cambridge, 1898. For general account of Rep- 

 tiles see H. Gadow, Amphibia and Reptiles (Cambridge Natural History), 

 Macmillan & Co., 1901 ; and C. K. Hoffmann, Reptilien, in Bronn's Klassen 

 u. Ordnungen des Thierreichs. 



